Browsing by Author "Chuu, DS"

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A Raman study of ZnSe at high pressure
(1997-06-01)
Chou, WC
;
Lin, CM
;
Ro, RS
;
Ho, CS
;
Hong, DY
The ZnSe was studied by Raman scattering spectroscopy at pressures up to 36 GPa at first time. The present researchers have found splittings of transverse optical (TO) phonon at 4.65 and 7.61 GPa. In addition, the Raman signals of the longitudinal optical (LO) phonon disappeared at 14.35 GPa. The disappearance of the LO phonon is attributed to the semiconductor-metal phase transition. However, the TO phonon peaks were still visible above the metallization pressure.
A Raman study of ZnSe at high pressure
(1997-06-01)
Chou, WC
;
Lin, CM
;
Ro, RS
;
Ho, CS
;
Hong, DY
The ZnSe was studied by Raman scattering spectroscopy at pressures up to 36 GPa at first time. The present researchers have found splittings of transverse optical (TO) phonon at 4.65 and 7.61 GPa. In addition, the Raman signals of the longitudinal optical (LO) phonon disappeared at 14.35 GPa. The disappearance of the LO phonon is attributed to the semiconductor-metal phase transition. However, the TO phonon peaks were still visible above the metallization pressure.
A simplification of entanglement purification
(2004-07-26)
Hsieh, JY
;
Li, CM
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
This study proposes a modification of existing entanglement purification protocols for pairs of qubits. The proposed protocol restores a desired pure state by standard purification local operations and classical communications, without preliminarily estimating the entangled state to be purified. The proposed protocol is demonstrated to outperform the previously proposed IBM and Oxford protocols. (C) 2004 Elsevier B.V. All rights reserved.
Alignment and orientation of absorbed dipole molecules
(2004-12-01)
Liao, YY
;
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Half-cycle laser pulse is applied on an absorbed molecule to investigate its alignment and orientation behavior. Crossover from field-free to hindered rotation motion is observed by varying the angel of hindrance of potential well. At small hindered angle, both alignment and orientation show sinusoidal-like behavior because of the suppression of higher excited states. However, mean orientation decreases monotonically as the hindered angle is increased, while mean alignment displays a minimum point at certain hindered angle. The reason is attributed to the symmetry of wave function and can be explained well by analyzing the coefficients of eigenstates.
Analysis of physical properties of III-nitride thin films by nanoindentation
(2003-06-01)
Jian, SR
;
Fang, TH
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The thin films of undoped GaN, GaN:Si, and Al0.12Ga0.88N on sapphire (0001) substrate using nanoindentation are investigated. The Young's modulus, hardness, and plastic energy of the films were calculated from the loading-unloading curve. The true hardness, maximum shear stress, and degree of elastic recovery are then deduced from the preceding calculated data. In addition, the loading-unloading curve clearly shows the pop-in phenomena, which can be attributed to the dislocation nucleation. To better understand the factors affecting the quality of films produced, the stress-strain relationship, which is able to reflect the quality of the fabricated films, is also analyzed using nanoindentation.
Analytical technique for simplification of the encoder-decoder circuit for a perfect five-qubit error correction
(2006-05-30)
Hsieh, JY
;
Li, CM
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Simpler encoding and decoding networks are necessary for more reliable quantum error-correcting codes (QECCs). The simplification of the encoder-decoder circuit for a perfect five-qubit QECC can be derived analytically if the QECC is converted from its equivalent one-way entanglement purification protocol. In this work, the analytical method to simplify the encoder-decoder circuit is introduced and a circuit that is as simple as the existing simplest circuits is presented as an example. The encoder-decoder circuit presented here involves nine single- and two-qubit unitary operations, only six of which are controlled-NOT gates.
Anderson model with spin-flip-associated tunneling
(2005-09-01)
Lin, KC
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The spin-flip-associated transport through a quantum dot based on the Anderson model in equilibrium and nonequilibrium situations is studied. It is found that electrons are scattered due to the spin-flip effect via the normal and the Kondo channels. Our results show that the conductance is suppressed due to the spin-flip effect, and the suppression due to the spin-flip scattering via the Kondo channel is stronger for temperatures below the Kondo temperature.
Anion-terminated zinc-blende CdS(100) surface
(1997-10-15)
Lin, CM
;
Tsai, MH
;
Yang, TJ
;
Chuu, DS
;
電子物理學系
Using the local-orbital density-functional molecular-dynamics method, we have studied the surface structure of the strain-stabilized zinc-blende monolayer anion-terrainated CdS(100) surface. By analogy with the GaAs(100) surface, we have considered four structural models and found that the structure with a (2 x 4) unit cell, in which there are a two-dimer unit and a two-shifted-dimer unit, is the most favorable. These results can be understood in terms of physical properties associated with ionicity.
Ballistic transport through coupled T-shaped quantum wires
(2004-05-01)
Lin, YK
;
Lin, KC
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The ballistic conductance of a coupled T-shaped semiconductor quantum wire (CTQW) is studied. Two types of CTQW are considered, one of which is a H-shaped quantum wire (PiQW) which consists of two vertical arms on the same side of the horizontal arm and the other a Pi-clone quantum wire (PiCQW) which consists of two vertical armes on the opposite sides of the horizontal arm. The mode matching method and Landauer-Buttiker theory are employed to study the energy dependence of the ballistic conductance. Most of transmission profiles of PiQW and PiCQW are found to be distinguishable for large separation d between the two vertical arms. The transmission probability manifests oscillatory behavior when d is increased. When a potential is applied to the connection region, it results in decoupling or coupling effects between the two T-shaped quantum wires according to whether it is positive or negative. When magnetic field is applied to CTQW, the transmission profiles are found to be affected prominently even if the electron passes through the field free region only. (C) 2003 Elsevier B.V. All rights reserved.
Bound state of the quantum dot formed at intersection of L- or T-shaped quantum wire in inhomogeneous magnetic field
(2002-03-01)
Lin, YK
;
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
A quantum dot (QD) can be formed at the intersection of the symmetric or asymmetric L-shaped (LQW) or T-shaped quantum wire (TQW). The bound state energies in such QD systems surrounded by inhomogeneous magnetic fields are found to depend strongly on the asymmetric parameter alpha=W-2/W-1, i.e., the ratio of the arm widths and magnetic field applied on the wire arms. Two effects of the magnetic field on the bound state energy of the electron can be obtained. One is the depletion effect which purges the electron out of the QD system. The other is to create an effective potential due to the quantized Landau levels of the magnetic field. Depletion effect is found to be more prominent in weak field region. Our results show the bound state energy of the electron in such QD system depends quadratically (linearly) on the magnetic field in the weak (strong) field region. It is also found that the bound state energy of the electron depends on the magnetic field strength only and not on its direction. A simple model is proposed to explain the behavior of the magnetic dependence of the bound state energy of the electron both in weak and strong magnetic field regions. The contour plots of the relative probability of the bound state in LQW or TQW in magnetic field are also presented. (C) 2002 American Institute of Physics.
Bound states of L- or T-shaped quantum wires in inhomogeneous magnetic fields
(2001-11-15)
Lin, YK
;
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The bound-state energies of L- or T-shaped quantum wires in inhomogeous magnetic fields are found to depend strongly on the asymmetric parameter alpha = W-2/W-1, i.e, the ratio of the arm widths. Two effects of magnetic field on bound-state energies of the electron are obtained. One is the depletion effect, which purges the electron out of the OQD system. The other is to create an effective potential due to quantized Landau levels of the magnetic field. The bound-state energies of the electron in L- or T-shaped quantum wires are found to depend quadratically (linearly) on the magnetic field in the weak- (strong-) field region and are independent of the direction of the magnetic field. A simple model is proposed to explain the behavior of the magnetic dependence of the bound-state energy in both weak- and strong-magnetic field regions.
Characteristics of transmission of electrons in a bent quantum waveguide with inhomogeneous magnetic fields
(1999-07-15)
Gu, BY
;
Lin, YK
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
We present numerical studies of the transmission properties in an L-shaped quantum waveguide (LQW) subject to an inhomogeneous magnetic field perpendicular to the LQW plane. The magnetic field remains zero at the corner region, thus, a magnetically defined cavity is formed in this LQW. We find that transmission characteristics of electrons in the LQW depend strongly on geometric parameters and magnetic configurations. Sharp peaks with unity amplitude and deep dips are observed in transmission as a function of the Fermi energy of the incident electron at some high fields. The mode-mode coupling between the wires and the cavity and multiple reflection of electrons in the cavity lead to the appearance of these structures in transmission spectrum. We also study the variation of transmission with magnetic field for different magnetic confinement configurations when fixing incident electron energy. In the magnetic depletion process of the propagating modes in wires, the transmission exhibits various patterns, such as stepped drop, wide valley, deep dips, large oscillations, or without any structure, sensitively dependent on incident electron energy and magnetic confinement configurations. It is expected that one can flexibly modify transmission spectrum of the LQW by applying an inhomogeneous magnetic field to match practical requirements. (C) 1999 American Institute of Physics. [S0021-8979(99)05714-X].
Characterization of CdTe film grown on a Si(111) substrate
(1998-02-01)
Pei, JH
;
Lin, CM
;
Chuu, DS
;
電子物理學系
;
物理研究所
We report the characterization of polycrystalline CdTe films grown on Si(111) by using UHV sublimination techniques. Films grown at substrate temperature below 250 degrees C exhibited streaked X-ray diffraction patterns. To understand the native oxide on the film surface, the films were exposed to a laboratory air environment in the growth chamber for several days. The XPS spectra were taken after each Ar-ion sputtering of these oxidized films. In order to obtain more information from the measured XPS data, we performed core-level line-shape analysis. Based on previously reported studies, CdTe, TeO2, and element Te are constituents in the film, while Cd is almost all in the CdTe state. Raman scattering from oxidized CdTe film in the frequency of 550-900 cm(-1) reveals that TeO2 is the predominant oxide.
Characterization of CdTe film grown on a Si(111) substrate
(1998-02-01)
Pei, JH
;
Lin, CM
;
Chuu, DS
;
電子物理學系
;
物理研究所
We report the characterization of polycrystalline CdTe films grown on Si(111) by using UHV sublimination techniques. Films grown at substrate temperature below 250 degrees C exhibited streaked X-ray diffraction patterns. To understand the native oxide on the film surface, the films were exposed to a laboratory air environment in the growth chamber for several days. The XPS spectra were taken after each Ar-ion sputtering of these oxidized films. In order to obtain more information from the measured XPS data, we performed core-level line-shape analysis. Based on previously reported studies, CdTe, TeO2, and element Te are constituents in the film, while Cd is almost all in the CdTe state. Raman scattering from oxidized CdTe film in the frequency of 550-900 cm(-1) reveals that TeO2 is the predominant oxide.
Characterization of self-assembled InAs quantum dots with InAlAs/InGaAs strain-reduced layers by photoluminescence spectroscopy
(2005-04-15)
Chang, KP
;
Yang, SL
;
Chuu, DS
;
Hsiao, RS
;
Chen, JF
The optoelectronic characteristics of self-assembled InAs quantum dots (QDs) with strain-reduced layers (SRLs) were investigated using photoluminescence (PL) spectroscopy. Various SRLs that combine In0.14Al0.86As and In0.14Ga0.86As with the same total thickness were examined to ascertain their confining effect on carriers in InAs QDs. The emission wavelength is blueshifted as the thickness of InAlAs is increased. The energy separation between the ground state and the first excited state of QDs with InAlAs SRLs greatly exceeds that of QDs with InGaAs SRLs. Atomic force microscopic images and PL spectra of the QD samples demonstrated that high-quality InAs QDs with long emission wavelengths and a large energy separation can be generated by growing a low-temperature, thin InAlAs SRL onto self-assembled QDs. (C) 2005 American Institute of Physics.
Collective excitations in a single-layer carbon nanotube
(1996-06-15)
Lin, MF
;
Chuu, DS
;
Huang, CS
;
Lin, YK
;
Shung, KWK
The inter-pi-band response function of a single-layer carbon nanotube is calculated within the random-phase approximation. Such a cylindrical system exhibits rich inter-pi-band excitations. The decoupled pi plasmons;of different angular momenta (L's) strongly depend on the transferred momenta (q's). Furthermore, they exhibit a dimensionality crossover as the nanotube radius is increased. For small q's and L's, the pi plasmon frequency is similar to 6-8 eV, which is insensitive to the nanotube geometry such as the radius and chiral angle. Comparison with recent experiments is discussed.
Collective excitations in graphite layers
(1997-09-01)
Huang, CS
;
Lin, MF
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The pi-electronic excitations in graphite layers are studied within the self-consistent-field approach. The pi plasmon behaves as an optical plasmon, mainly due to the pi-band characteristics. The excitation spectra and the pi-plasmon frequencies are obviously enhanced by the interlayer Coulomb interactions and increase with the number of graphite layers. (C) 1997 Published by Elsevier Science Ltd.
Cooperative behavior of RVB, flux phase, and antiferromagnetic states
(1997-04-20)
Chiueh, HL
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The coexistence of RVB, flux phase, and antiferromagnetic states for the t-J model is studied within the frame work of the mean-field theory by means of the slave-boson approach. Two simple relations among these three order parameters manifesting the cooperative behavior of these states are derived. A phase diagram separating the antiferromagnetic from the non-antiferromagnetic stale is obtained. Comparison with available previous work shows that our result agrees reasonably well. (C) 1997 Elsevier Science B.V.
Current detection of superradiance and induced entanglement of double quantum dot excitons
(2003-04-25)
Chen, YN
;
Chuu, DS
;
Brandes, T
;
電子物理學系
;
Department of Electrophysics
We propose to measure the superradiance effect by observing the current through a semiconductor double-dot system. An electron and a hole are injected separately into one of the quantum dots to form an exciton and then recombine radiatively. We find that the stationary current shows oscillatory behavior as one varies the interdot distance. The amplitude of oscillation can be increased by incorporating the system into a microcavity. Furthermore, the current is suppressed if the dot distance is small compared to the wavelength of the emitted photon. This photon trapping phenomenon generates the entangled state and may be used to control the emission of single photons at predetermined times.
Decay rate and renormalized frequency shift of a quantum wire Wannier exciton in a planar microcavity
(2001-09-15)
Chen, YN
;
Chuu, DS
;
Brandes, T
;
Kramer, B
;
電子物理學系
Super-radiant decay rate and frequency shift of a Wannier exciton in a one-dimensional quantum wire are studied. It is shown that the dark-mode exciton can be examined experimentally when the quantum wire is embedded in a planar microcavity. It is also found that the decay rate is greatly enhanced as the cavity length L-c is equal to the multiple wavelength of the emitted photon. Similar to its decay-rate counterpart, the frequency shift also shows discontinuities at resonant modes.